Sedlacek, who graduated from a military academy, fled to France in 1940 when his nation was occupied by Nazi troops. After France was defeated, he joined the British army before moving to the Soviet Union in 1944 and helping liberate Czechoslovakia.

After the Communists took power there, he was arrested in 1951, convicted of anti-communist activities and jailed for life. He was released in 1960 and exonerated by the Czech Velvet Revolution in 1989.